Gas Optimizations - Githubissues

Summary

G-01 State variables only set in the constructor should be declared immutable | 4 instances G-02 += costs more gas than = + for state variables | 9 instances G-03 internal functions only called once can be inlined to save gas | 2 instances G-04 Cache array length before loop | 2 instances G-05 Using bools for storage incurs overhead | 2 instances G-06 Use a more recent version of solidity | 19 instances G-07 Use != 0 instead of > 0 | 1 instances G-08 Redundant zero initialization | 7 instances G-09 Use prefix not postfix in loops | 2 instances G-10 Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead | 44 instances G-11 Using private rather than public for constants, saves gas | 13 instances G-12 Empty blocks should be removed or emit something | 3 instances G-13 Functions guaranteed to revert when called by normal users can be marked payable | 5 instances G-14 Public functions to external | 8 instances G-15 Use calldata instead of memory for function parameters | 3 instances G-16 Use simple comparison in trinary logic / in if statement | 4 instances G-17 ++i costs less gas compared to i++ or i += 1 | 2 instances

Total: 130 instances in 17 issues

G-01 State variables only set in the constructor should be declared immutable

Avoids a Gsset (20000 gas) in the constructor, and replaces each Gwarmacces (100 gas) with a PUSH32 (3 gas).

4 instances in 2 files:

utils/token/GobblersERC721.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L23 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L25

utils/token/PagesERC721.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/PagesERC721.sol#L24 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/PagesERC721.sol#L26

G-02 += costs more gas than = + for state variables

9 instances in 3 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L439 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L456 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L464 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L662 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L844 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L912 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L913

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L244

GobblersERC721.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L184

G-03 internal functions only called once can be inlined to save gas

Not inlining costs 20 to 40 gas because of two extra JUMP instructions and additional stack operations needed for function calls.

2 instances in 2 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L813-L817

token/GobblersERC721.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L174-L178

G-04 Cache array length before loop (see .length)

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack. Caching the array length in the stack saves around 3 gas per iteration.

Recommended Mitigation Steps: I suggest storing the array’s length in a variable before the for-loop, and use it instead

2 instances in 2 files:

token/GobblersERC1155B.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L114

/utils/GobblerReserve.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L37

G-05 Using bools for storage incurs overhead

Booleans are more expensive than uint256 or any type that takes up a full word because each write operation emits an extra SLOAD to first read the slot's contents, replace the bits taken up by the boolean, and then write back.

This is the compiler's defense against contract upgrades and pointer aliasing, and it cannot be disabled. https://github.com/OpenZeppelin/openzeppelin-contracts/blob/58f635312aa21f947cae5f8578638a85aa2519f5/contracts/security/ReentrancyGuard.sol#L23-L27

Recommended Mitigation Steps: Use uint256(1) and uint256(2) for true/false

2 instances in 2 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L149

tokens/ERC721.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/tokens/ERC721.sol#L51

G-06 Use a more recent version of solidity

Use a solidity version of at least 0.8.0 to get overflow protection without SafeMath Use a solidity version of at least 0.8.2 to get compiler automatic inlining Use a solidity version of at least 0.8.3 to get better struct packing and cheaper multiple storage reads Use a solidity version of at least 0.8.4 to get custom errors, which are cheaper at deployment than revert()/require() strings Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value. Use a solidity version of at least 0.8.12 to get string.concat() instead of abi.encodePacked(,). Use a solidity version of at least 0.8.13 to get the ability to use using for with a list of free functions

19 instances in 19 files:

https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Goo.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/PagesERC721.sol#L2

https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/tokens/ERC721.sol#L2 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/auth/Owned.sol#L2 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/MerkleProofLib.sol#L2 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/LibString.sol#L2 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/FixedPointMathLib.sol#L2 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/SignedWadMath.sol#L2

https://github.com/transmissions11/goo-issuance/blob/648e65e66e43ff5c19681427e300ece9c0df1437/src/LibGOO.sol#L2 https://github.com/transmissions11/VRGDAs/blob/f4dec0611641e344339b2c78e5f733bba3b532e0/src/VRGDA.sol#L2 https://github.com/transmissions11/VRGDAs/blob/f4dec0611641e344339b2c78e5f733bba3b532e0/src/LogisticVRGDA.sol#L2 https://github.com/transmissions11/VRGDAs/blob/f4dec0611641e344339b2c78e5f733bba3b532e0/src/LinearVRGDA.sol#L2

https://github.com/code-423n4/2022-09-artgobblers/blob/main/script/deploy/DeployBase.s.sol#L2 https://github.com/code-423n4/2022-09-artgobblers/blob/main/script/deploy/DeployRinkeby.s.sol#L2

G-07 Use != 0 instead of > 0

Using > 0 uses slightly more gas than using != 0. Use != 0 when comparing uint variables to zero, which cannot hold values below zero.

Recommended Mitigation Steps: Use != 0 instead of > 0. This change saves 6 gas per instance

1 instance in 1 file:

utils/SignedWadMath.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/SignedWadMath.sol#L142

G-08 Redundant zero initialization

Solidity does not recognize null as a value, so uint variables are initialized to zero. Setting a uint variable to zero is redundant and can waste gas. There are several places where an int is initialized to zero, which looks like: uint256 amount = 0;

Recommended Mitigation Steps: Remove the redundant zero initialization uint256 amount; ( / or: If a variable is not set/initialized, it is assumed to have the default value (0 for uint, false for bool, address(0) for address…). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

7 instances in 5 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L432 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L592

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L251

utils/token/GobblersERC1155B.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L114 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L173

utils/GobblerReserve.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L37

utils/token/GobblersERC721.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC721.sol#L186

G-09 Use prefix not postfix in loops

Using a prefix increment (++i) instead of a postfix increment (i++) saves gas for each loop cycle and so can have a big gas impact when the loop executes on a large number of elements. Saves 6 gas PER LOOP

2 instances in 2 files:

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L251

utils/GobblerReserve.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L37

G-10 Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead

When using elements that are smaller than 32 bytes, your contract’s gas usage may be higher. This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller than that, the EVM must use more operations in order to reduce the size of the element from 32 bytes to the desired size. https://docs.soliditylang.org/en/v0.8.11/internals/layout_in_storage.html

Use a larger size then downcast where needed

44 instances in 3 files:

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L244 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L253

G-11 Using private rather than public for constants, saves gas

If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table

13 instances in 2 files:

script/deploy/DeployRinkeby.s.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/script/deploy/DeployRinkeby.s.sol#L13 https://github.com/code-423n4/2022-09-artgobblers/blob/main/script/deploy/DeployRinkeby.s.sol#L14 https://github.com/code-423n4/2022-09-artgobblers/blob/main/script/deploy/DeployRinkeby.s.sol#L15

G-12 Empty blocks should be removed or emit something

The code should be refactored such that they no longer exist, or the block should do something useful, such as emitting an event or reverting. If the contract is meant to be extended, the contract should be abstract and the function signatures be added without any default implementation. If the block is an empty if-statement block to avoid doing subsequent checks in the else-if/else conditions, the else-if/else conditions should be nested under the negation of the if-statement, because they involve different classes of checks, which may lead to the introduction of errors when the code is later modified (if(x){}else if(y){...}else{...} => if(!x){if(y){...}else{...}})

3 instances in 2 files:

utils/MerkleProofLib.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/MerkleProofLib.sol#L23 (2)

utils/LibString.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/LibString.sol#L30

G-13 Functions guaranteed to revert when called by normal users can be marked payable

If a function modifier such as onlyOwner is used, the function will revert if a normal user tries to pay the function. Marking the function as payable will lower the gas cost for legitimate callers because the compiler will not include checks for whether a payment was provided.

The extra opcodes avoided are CALLVALUE(2),DUP1(3),ISZERO(3),PUSH2(3),JUMPI(10),PUSH1(3),DUP1(3),REVERT(0),JUMPDEST(1),POP(2), which costs an average of about 21 gas per call to the function, in addition to the extra deployment cost.

5 instances in 3 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L560

Goo.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Goo.sol#L101 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Goo.sol#L108 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Goo.sol#L115

GobblerReserve.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L34

G-14 Public functions to external

Public functions not called by the contract should be declared external instead. Contracts are allowed to override their parents’ functions and change the visibility from external to public and can save gas by doing so. https://docs.soliditylang.org/en/latest/contracts.html#function-overriding

8 instances in 4 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L693

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L265

utils/token/GobblersERC1155B.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L55

utils/token/GobblersERC1155B.so https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L79 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L85 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L93 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L101 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L124

G-15 Use calldata instead of memory for function parameters

Having function arguments use calldata instead of memory can save gas.

Recommended Mitigation Steps: Change function arguments from memory to calldata.

3 instances in 2 files:

utils/token/GobblersERC1155B.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L138 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/token/GobblersERC1155B.sol#L161

tokens/ERC721.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/tokens/ERC721.sol#L207

G-16 Use simple comparison in trinary logic / in if statement

The comparison operators >= and <= use more gas than >, <, or ==. Replacing the >= and ≤ operators with a comparison operator that has an opcode in the EVM saves gas.

Recommended Mitigation Steps: Replace the comparison operator and reverse the logic to save gas using the suggestions above.

4 instances in 2 files:

ArtGobblers.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L435 https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/ArtGobblers.sol#L497

utils/SignedWadMath.sol https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/SignedWadMath.sol#L86 https://github.com/transmissions11/solmate/blob/bff24e835192470ed38bf15dbed6084c2d723ace/src/utils/SignedWadMath.sol#L90

G-17 ++i costs less gas compared to i++ or i += 1

++i costs less gas compared to i++ or i += 1 for unsigned integer, as pre-increment is cheaper (about 5 gas per iteration). This statement is true even with the optimizer enabled. i++ increments i and returns the initial value of i. Which means: uint i = 1; i++; // == 1 but i == 2 But ++i returns the actual incremented value: uint i = 1; ++i; // == 2 and i == 2 too, so no need for a temporary variable . In the first case, the compiler has to create a temporary variable (when used) for returning 1 instead of 2.

Recommended Mitigation Steps: I suggest using ++i instead of i++ to increment the value of an uint variable.

2 instances in 2 files:

Pages.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/Pages.sol#L251

utils/GobblerReserve.sol https://github.com/code-423n4/2022-09-artgobblers/blob/main/src/utils/GobblerReserve.sol#L37

code-423n4 / 2022-09-artgobblers-findings

Gas Optimizations #459

Summary

G-01 State variables only set in the constructor should be declared immutable

G-02 += costs more gas than = + for state variables

G-03 internal functions only called once can be inlined to save gas

G-04 Cache array length before loop (see .length)

G-05 Using bools for storage incurs overhead

G-06 Use a more recent version of solidity

G-07 Use != 0 instead of > 0

G-08 Redundant zero initialization

G-09 Use prefix not postfix in loops

G-10 Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead

G-11 Using private rather than public for constants, saves gas

G-12 Empty blocks should be removed or emit something

G-13 Functions guaranteed to revert when called by normal users can be marked payable

G-14 Public functions to external

G-15 Use calldata instead of memory for function parameters

G-16 Use simple comparison in trinary logic / in if statement

G-17 ++i costs less gas compared to i++ or i += 1